C++ BlockBegin::pred_at方法代码示例

bool ShortLoopOptimizer::process(BlockBegin* loop_header) {
  TRACE_VALUE_NUMBERING(tty->print_cr("** loop header block"));

  _too_complicated_loop = false;
  _loop_blocks.clear();
  _loop_blocks.append(loop_header);

  for (int i = 0; i < _loop_blocks.length(); i++) {
    BlockBegin* block = _loop_blocks.at(i);
    TRACE_VALUE_NUMBERING(tty->print_cr("processing loop block B%d", block->block_id()));

    if (block->is_set(BlockBegin::exception_entry_flag)) {
      // this would be too complicated
      return false;
    }

    // add predecessors to worklist
    for (int j = block->number_of_preds() - 1; j >= 0; j--) {
      BlockBegin* pred = block->pred_at(j);

      if (pred->is_set(BlockBegin::osr_entry_flag)) {
        return false;
      }

      ValueMap* pred_map = value_map_of(pred);
      if (pred_map != NULL) {
        current_map()->kill_map(pred_map);
      } else if (!_loop_blocks.contains(pred)) {
        if (_loop_blocks.length() >= ValueMapMaxLoopSize) {
          return false;
        }
        _loop_blocks.append(pred);
      }
    }

    // use the instruction visitor for killing values
    for (Value instr = block->next(); instr != NULL; instr = instr->next()) {
      instr->visit(this);
      if (_too_complicated_loop) {
        return false;
      }
    }
  }

  bool optimistic = this->_gvn->compilation()->is_optimistic();

  if (UseLoopInvariantCodeMotion && optimistic) {
    LoopInvariantCodeMotion code_motion(this, _gvn, loop_header, &_loop_blocks);
  }

  TRACE_VALUE_NUMBERING(tty->print_cr("** loop successfully optimized"));
  return true;
}

GlobalValueNumbering::GlobalValueNumbering(IR* ir)
    : _current_map(NULL)
    , _value_maps(ir->linear_scan_order()->length(), NULL)
{
    TRACE_VALUE_NUMBERING(tty->print_cr("****** start of global value numbering"));

    ShortLoopOptimizer short_loop_optimizer(this);
    int subst_count = 0;

    BlockList* blocks = ir->linear_scan_order();
    int num_blocks = blocks->length();

    BlockBegin* start_block = blocks->at(0);
    assert(start_block == ir->start() && start_block->number_of_preds() == 0 && start_block->dominator() == NULL, "must be start block");
    assert(start_block->next()->as_Base() != NULL && start_block->next()->next() == NULL, "start block must not have instructions");

    // initial, empty value map with nesting 0
    set_value_map_of(start_block, new ValueMap());

    for (int i = 1; i < num_blocks; i++) {
        BlockBegin* block = blocks->at(i);
        TRACE_VALUE_NUMBERING(tty->print_cr("**** processing block B%d", block->block_id()));

        int num_preds = block->number_of_preds();
        assert(num_preds > 0, "block must have predecessors");

        BlockBegin* dominator = block->dominator();
        assert(dominator != NULL, "dominator must exist");
        assert(value_map_of(dominator) != NULL, "value map of dominator must exist");

        // create new value map with increased nesting
        _current_map = new ValueMap(value_map_of(dominator));

        if (num_preds == 1) {
            assert(dominator == block->pred_at(0), "dominator must be equal to predecessor");
            // nothing to do here

        } else if (block->is_set(BlockBegin::linear_scan_loop_header_flag)) {
            // block has incoming backward branches -> try to optimize short loops
            if (!short_loop_optimizer.process(block)) {
                // loop is too complicated, so kill all memory loads because there might be
                // stores to them in the loop
                current_map()->kill_memory();
            }

        } else {
            // only incoming forward branches that are already processed
            for (int j = 0; j < num_preds; j++) {
                BlockBegin* pred = block->pred_at(j);
                ValueMap* pred_map = value_map_of(pred);

                if (pred_map != NULL) {
                    // propagate killed values of the predecessor to this block
                    current_map()->kill_map(value_map_of(pred));
                } else {
                    // kill all memory loads because predecessor not yet processed
                    // (this can happen with non-natural loops and OSR-compiles)
                    current_map()->kill_memory();
                }
            }
        }

        if (block->is_set(BlockBegin::exception_entry_flag)) {
            current_map()->kill_exception();
        }

        TRACE_VALUE_NUMBERING(tty->print("value map before processing block: "); current_map()->print());

        // visit all instructions of this block
        for (Value instr = block->next(); instr != NULL; instr = instr->next()) {
            assert(!instr->has_subst(), "substitution already set");

            // check if instruction kills any values
            instr->visit(this);

            if (instr->hash() != 0) {
                Value f = current_map()->find_insert(instr);
                if (f != instr) {
                    assert(!f->has_subst(), "can't have a substitution");
                    instr->set_subst(f);
                    subst_count++;
                }
            }
        }

        // remember value map for successors
        set_value_map_of(block, current_map());
    }

    if (subst_count != 0) {
        SubstitutionResolver resolver(ir);
    }

    TRACE_VALUE_NUMBERING(tty->print("****** end of global value numbering. "); ValueMap::print_statistics());
}

bool FpuStackAllocator::merge_fpu_stack_with_successors(BlockBegin* block) {
#ifndef PRODUCT
  if (TraceFPUStack) {
    tty->print_cr("Propagating FPU stack state for B%d at LIR_Op position %d to successors:",
                  block->block_id(), pos());
    sim()->print();
    tty->cr();
  }
#endif

  bool changed = false;
  int number_of_sux = block->number_of_sux();

  if (number_of_sux == 1 && block->sux_at(0)->number_of_preds() > 1) {
    // The successor has at least two incoming edges, so a stack merge will be necessary
    // If this block is the first predecessor, cleanup the current stack and propagate it
    // If this block is not the first predecessor, a stack merge will be necessary

    BlockBegin* sux = block->sux_at(0);
    intArray* state = sux->fpu_stack_state();
    LIR_List* instrs = new LIR_List(_compilation);

    if (state != NULL) {
      // Merge with a successors that already has a FPU stack state
      // the block must only have one successor because critical edges must been split
      FpuStackSim* cur_sim = sim();
      FpuStackSim* sux_sim = temp_sim();
      sux_sim->read_state(state);

      merge_fpu_stack(instrs, cur_sim, sux_sim);

    } else {
      // propagate current FPU stack state to successor without state
      // clean up stack first so that there are no dead values on the stack
      if (ComputeExactFPURegisterUsage) {
        FpuStackSim* cur_sim = sim();
        ResourceBitMap live_fpu_regs = block->sux_at(0)->fpu_register_usage();
        assert(live_fpu_regs.size() == FrameMap::nof_fpu_regs, "missing register usage");

        merge_cleanup_fpu_stack(instrs, cur_sim, live_fpu_regs);
      }

      intArray* state = sim()->write_state();
      if (TraceFPUStack) {
        tty->print_cr("Setting FPU stack state of B%d (merge path)", sux->block_id());
        sim()->print(); tty->cr();
      }
      sux->set_fpu_stack_state(state);
    }

    if (instrs->instructions_list()->length() > 0) {
      lir()->insert_before(pos(), instrs);
      set_pos(instrs->instructions_list()->length() + pos());
      changed = true;
    }

  } else {
    // Propagate unmodified Stack to successors where a stack merge is not necessary
    intArray* state = sim()->write_state();
    for (int i = 0; i < number_of_sux; i++) {
      BlockBegin* sux = block->sux_at(i);

#ifdef ASSERT
      for (int j = 0; j < sux->number_of_preds(); j++) {
        assert(block == sux->pred_at(j), "all critical edges must be broken");
      }

      // check if new state is same
      if (sux->fpu_stack_state() != NULL) {
        intArray* sux_state = sux->fpu_stack_state();
        assert(state->length() == sux_state->length(), "overwriting existing stack state");
        for (int j = 0; j < state->length(); j++) {
          assert(state->at(j) == sux_state->at(j), "overwriting existing stack state");
        }
      }
#endif
#ifndef PRODUCT
      if (TraceFPUStack) {
        tty->print_cr("Setting FPU stack state of B%d", sux->block_id());
        sim()->print(); tty->cr();
      }
#endif

      sux->set_fpu_stack_state(state);
    }
  }

#ifndef PRODUCT
  // assertions that FPU stack state conforms to all successors' states
  intArray* cur_state = sim()->write_state();
  for (int i = 0; i < number_of_sux; i++) {
    BlockBegin* sux = block->sux_at(i);
    intArray* sux_state = sux->fpu_stack_state();

    assert(sux_state != NULL, "no fpu state");
    assert(cur_state->length() == sux_state->length(), "incorrect length");
    for (int i = 0; i < cur_state->length(); i++) {
      assert(cur_state->at(i) == sux_state->at(i), "element not equal");
    }
  }
//.........这里部分代码省略.........